In dynamic testing a specimen of material is subjected to a variety of test loads. These include, e.g., tension, compression, and torsion, and some of these loads are under certain test conditions applied simultaneously to a specimen. The grips which secure a test specimen to permit the test machine to apply loads to the specimen are very important. A problem has been creation of unwanted, nonuniform stresses and strains in the specimen because of the way the grips are secured to it. For example, specimens have often been fabricated with threaded or button-shaped ends in order to be securely held by the grips. Machining of these specimen ends is time-consuming and difficult and introduces stress raisers in the specimen. Gripping of the preformed ends induces shear forces through the threaded or button ends of the specimen, leading to nonuniform stresses and strains and possible errors in the test results. It would be desirable to have a grip that does not require such preforming of the specimen ends, readily aligns the specimen, and grips it evenly and uniformly as well as strongly enough to permit the specimen to undergo severe testing.
My U.S. Pat. No. 3,224,259 describes a specimen grip in which a pair of externally wedge-shaped flat jaws ride against an internally oppositely wedge-shaped U-type flat frame whereby the force of the jaws' grip on a specimen is increased during operation as the jaws move relative to the frame and interact therewith through contacting wedging surfaces.
Stratienko U.S. Pat. No. 3,501,183 shows the use of a pair of axially interlocking wedges for securing a shaft to a surrounding member such as a gear or another shaft.
Stratienko U.S. Pat. No. 3,368,834 shows the use of a pair of radially and axially interlocking wedges for the same purpose as the first named Stratienko patent.